1. Field of the Invention
The present invention relates to a mechanism for adjustable installation of a band plate-like member to orient the face of the band plate-like member, such as a reflector, in a predetermined direction. More particularly, the present invention relates to a mechanism for adjustable installation of a band plate-like member, which is suitable for adjusting the orientation of the reflecting face of a reflector used with an optical scanner or a cylindrical mirror for reflecting a beam of light incident upon an image carrier such as a photosensitive drum.
2. Description of the Related Art
An optical scanner used with an image forming apparatus, such as copying machines or printers, is adapted such that a laser beam emitted from a laser source and including image information is dimmed appropriately and impinges upon deflecting means such as a polygon mirror. Then, an image carrier such as a photosensitive drum is radiated with the deflected laser beam to form an electrostatic latent image on the surface thereof. The electrostatic latent image is then developed with toner to form a toner image, which, in turn, is transferred onto a transfer medium such as recording paper to form an image. Also known is a tandem image forming apparatus for a color image forming apparatus such as a color copying machine or a color printer. The reproduction scanning method is performed with laser beams including yellow (Y), magenta (M), cyan (C), and black (BK) image data scanned along a straight line, across a plurality of image carriers such as photosensitive drums, arranged side by side, to form an electrostatic latent image on each of the image carriers. Then, the electrostatic latent image is developed with a predetermined toner to form a toner image, which is in turn transferred successively onto a transfer medium such as recording paper, adapted to move in the direction of the side-by-side arrangement of the image carriers, in order to form a color image. Incidentally, the direction in which a beam of light is deflected with deflecting means such as a polygon mirror to form an electrostatic latent image is defined as the main scan direction, while the direction in which an electrostatic latent image is formed through the rotation of the photosensitive drums acting as image carriers is defined as a sub scan direction.
In recent years, it has been required to provide a plurality of beams of light and scan units for scanning use to introduce color and the higher-speed copying machine or the printers. In order to secure the sharpness of images to be formed, it is necessary to implement the desired optical characteristics of the plurality of scan beams and the desired scan characteristics of the scan unit as well as uniform characteristics of the plurality of units. To implement the optical and scan characteristics, the optical components constituting the optical scanner have to be assembled with high accuracy so that each of the optical components is sustained in place. A slight displacement or a variation in assembly of the reflector in the direction of reflection would cause the optical or scan characteristics to deteriorate. It is therefore necessary to adjust the direction of reflection of the reflector with high accuracy. The reflector for reflecting a scan beam reflected on a polygon mirror is formed in a band plate shape and supported at the both ends to cover the scan area, and a variation in assembly at one end would thus cause the reflecting face to be oriented in a totally different direction. It is therefore necessary to adjust the assembly of the both ends with high accuracy.
For example, conventionally known, as a mechanism of this type for adjusting a reflector is a mechanism for adjusting a mirror, disclosed in Japanese Utility Model Laid-Open Publication No. 1993-33108. This mirror adjustment mechanism is provided at the ends of the mirror frame with support pieces that can abut against the side of the reflecting face of the mirror. The support piece is provided pivotably with an adjustment plate that can abut against the side of the reflecting face of the mirror. In addition, the adjustment plate is provided with an adjustment member for adjusting the pivotal position thereof and an energizing member for pressing against the mirror in contact with the rear side of the mirror frame. Then, when the adjustment member is adjusted to allow the adjustment plate to pivot, the mirror swings about the longitudinal direction as its axis to cause the reflecting face to be oriented in a different direction.
On the other hand, disclosed in Japanese Patent Laid-Open Publication No. 1994-148490 is a mechanism for holding the optical member of a beam scan optical system. This mechanism for holding the optical member employs the following configuration. That is, provided are holes having small projections on the side plate of the housing such as of an optical apparatus. Both ends of a plane mirror are fitted loosely into these holes. A presser plate is fixedly screwed from outside onto the side plate but made pivotable about a fulcrum that is different from the fixing screw. A presser piece provided on the presser plate is brought into contact with the rear side of the mirror. The presser plate is pivoted to adjust the angle of inclination of the mirror and then fixed to the side plate with a fixing screw. A long hole formed on the presser plate and an eccentric pin are combined with each other to allow the eccentric pin to pivot, thereby pivoting the presser plate.
In some cases, a reflector is provided at the final stage, for guiding a beam of light to the image carrier of the optical scanner, which is provided with a long cylindrical mirror having a cylindrical surface in order to adjust the mirror so that the beam of light is incident on the surface of the image carrier under a predetermined magnification. In this cylindrical mirror, its displacement in the normal direction causes a variation in magnification on the surface of the image carrier. Furthermore, pivotal movement of the mirror about the direction parallel to the center of its curvature as its axis causes a variation in the position of incidence of the beam on the image carrier. A shift in relative position between both ends of the mirror causes the position of the scan line to vary in the main scan direction. Accordingly, in the cylindrical mirror, it is necessary to adjust its position in the normal direction (hereinafter referred to as the “magnification adjustment”), the pivotal angle to thereby adjust the position of incidence (hereinafter referred to as the “register adjustment”), and the relative position between both ends (hereinafter referred to as the “skew adjustment”). This mechanism for adjustable installation of the cylindrical mirror also employs the aforementioned conventional mirror adjustment mechanism and the mechanism for holding optical members.
On the other hand, the mechanism for adjusting a mirror, disclosed in Japanese Utility Model Laid-Open Publication No. 1993-33108, allows the adjustment plate in direct contact with the mirror to pivot. Since this adjustment plate is provided at either one end or both ends of the mirror, it is possible to cause strain such as twist or bend to occur in the mirror depending on the method of the adjustment. That is, the mechanism having an adjustment plate disposed at the one end of the mirror allows the other end to be restrained by a predetermined force. Accordingly, when the adjustment plate is pivoted to movably push the one end, the mirror will be possibly bent or twisted. On the other hand, the mechanism provided with the adjustment plate on both ends requires adjustment at both ends of the mirror. This will make the adjustment irksome and the strain of the mirror cannot be securely prevented unless the mirror is adjusted evenly at both ends.
A mechanism for holding optical members is disclosed in Japanese Patent Laid-Open Publication No. 1994-148490 and allows the presser plate, acting as a plate spring and pushing resiliently on the rear side of the mirror, to be in contact with both ends of the mirror. Accordingly, like said mirror adjustment mechanism, the presser plate pressed against the one end is adjusted to thereby cause the mirror to be bent or twisted by the force of the adjustment, thus causing strain to occur.